Porous inorganic carrier and method for producing nucleic acid using same

ABSTRACT

An inorganic porous carrier including a linker of formula (1), wherein a mode diameter in a pore distribution is 0.04 μm to 1 μm, and a predetermined cumulative pore volume ratio is 30% or less [a bond * represents a linkage to the oxygen atom of a silanol group in an inorganic porous substance; n is an integer; R represents independently of each other an alkyl group containing 3 to 10 carbon atoms which may optionally have a substituent such as an alkoxy group; and L represents a single bond; an alkylene group of 1 to 20 carbon atoms; or an alkylene group containing 2 to 20 carbon atoms which contains —CH 2 -Q-CH 2 — group wherein any group Q selected from a group consisting of —O— etc. is inserted into at least one of —CH 2 —CH 2 — group constituting the alkylene group]; and a method for preparing a nucleic acid using the same.

TECHNICAL FIELD

This application claims priority to and the benefit of Japanese PatentApplication No. 2019-067995 filed on Mar. 29, 2019, the entire contentsof which are incorporated herein by reference.

The present invention relates to an inorganic porous carrier, and amethod for preparing nucleic acid using the same.

BACKGROUND ART

As a method for chemically synthesizing a nucleic acid, a solid-phasesynthesis method according to a phosphoramidite method is widely used.In this method, first, a functional group such as an amino group isintroduced onto an inorganic porous substance by a silane coupling agentor the like, and a nucleoside providing a 3′end of the nucleic acid isbound to the functional group. Then, a nucleic acid elongation reactionis carried out on the solid-phase support by starting from thenucleoside.

In the solid-phase synthesis method, when a strand length of the nucleicacid to be synthesized becomes long, a synthesis efficiency drasticallydecreases, and consequently, a large amount of by-products (that is, asubstance having shorter strand length than a target strand length) isprone to be produced and mixed. It is considered that this phenomenon iscaused by closing a pore when a nucleic acid molecule is elongated in apore of a porous carrier, resulting in an inhibition of elongationreaction, side reactions, or the like.

As a technique for preventing a closure of a pore due to an elongationof a nucleic acid molecule, it has been proposed that a swelling polymeris covered on the surface of an inorganic porous substance (see Patentdocument 1).

CITATION LIST Patent Document

-   Patent Document 1: US 2009/0005536 A1

SUMMARY OF THE INVENTION Problems to be Solved by Invention

In general, as a nucleic acid to be synthetized is longer, a closure ofa pore has a tendency to be happened, and as a result, a purity onnucleic acid synthesis has a tendency to be decreased. In particular,when a long-strand nucleic acid having 40 mer or more is synthesized, ina case of using conventional solid-phase carrier, a nucleic acid havingshort strand length than a nucleic acid having a target strand lengthhas a tendency to be produced, and as a result, a purity of the longlength nucleic acid becomes a problem.

The present invention has been made in view of the above situation, andthe problem to be solved by the present invention is to provide aninorganic porous carrier which can improve the purity in the preparationof nucleic acid, and a method for preparing a nucleic acid using thesame.

Means to Solve Problems

In order to solve the above problem, the present invention have thefollowing constituent aspects.

That is, in the first aspect of the present invention, the inventionprovides an inorganic porous carrier that comprises a linker representedby general formula (1), wherein a most frequent value (mode diameter) ina pore distribution as measured by mercury intrusion method is 0.04 μmto 1 μm, and also a cumulative pore volume ratio of cumulative porevolume (VB) whose pore size being within a range of 0.004 μm to 0.04 μmrelative to cumulative pore volume (VA) whose pore size being within arange of 0.04 μm to 1 μm is 30% or less.

[wherein,

a bond marked with * represents a linkage to the oxygen atom of asilanol group in an inorganic porous substance;

n is an integer of 1, 2 or 3;

R represents independently of each other an alkyl group containing 3 to10 carbon atoms which may optionally have a substituent selected from analkoxy group and a fluorine atom; a phenyl group which may optionallyhave a substituent selected from an alkyl group, an alkoxy group, and afluorine atom; a hydroxyl group; or an alkoxy group containing 1 to 4carbon atom; and

L represents a single bond; an alkylene group of 1 to 20 carbon atoms;or an alkylene group containing 2 to 20 carbon atoms which contains—CH₂-Q-CH₂— group wherein any group Q selected from a group consistingof —O—, —NH—, —NH—CO— and —NH—CO—NH— is inserted into at least one of—CH₂—CH₂— group constituting the alkylene group; providing that a carbonatom of the methylene group bound to the group Q does not bind toanother group Q at the same time].

In the second aspect of the present invention, the invention provides aninorganic porous carrier that comprises a linker represented by generalformula (2), wherein a mode diameter in a pore distribution as measuredby mercury intrusion method is 0.04 μm to 1 μm, and also a cumulativepore volume ratio of cumulative pore volume (VS) whose pore size beingwithin a range of 0.004 μm to 0.04 μm relative to cumulative pore volume(VA) whose pore size being within a range of 0.04 μm to 1 μm is 30% orless (hereinafter, the inorganic porous carrier may be referred to as“Solid-phase carrier”).

[wherein

a bond marked with * represents a linkage to the oxygen atom of asilanol group in an inorganic porous substance;

n is an integer of 1, 2 or 3;

R represents independently of each other an alkyl group containing 3 to10 carbon atoms which may optionally have a substituent selected from analkoxy group and a fluorine atom; a phenyl group which may optionallyhave a substituent selected from an alkyl group, an alkoxy group, and afluorine atom; a hydroxyl group; or an alkoxy group containing 1 to 4carbon atom;

L represents a single bond; an alkylene group containing 1 to 20 carbonatoms; or an alkylene group containing 2 to 20 carbon atoms whichcontains —CH₂-Q-CH₂— group wherein any group Q selected from the groupconsisting of —O—, —NH—, —NH—CO—, and —NH—CO—NH— is inserted into atleast one —CH₂—CH₂— group constituting the alkylene group; providingthat a carbon atom of the methylene group bound to the group Q doses notbind to another group Q at the same time;

R_(b) represents a nucleotide or a nucleotide in which a reactive groupis protected or deprotected; and

L₁ represents a divalent group bound to an oxygen atom of a primary or asecondary hydroxy group as R_(b).].

According to a certain one embodiment of the second aspect of thepresent invention, L¹ in the general formula (2) may be a succinyllinker or a universal linker.

According to a certain one embodiment of the second aspect of thepresent invention, the specific surface area per volume of theabove-mentioned inorganic porous substance may be within a range of 0.1m²/mL or more to 100 m²/mL or less.

According to a certain one embodiment of the second aspect of thepresent invention, the pore volume per volume of the above-mentionedinorganic porous substance may be within a range of 0.05 mL/mL or moreto 0.6 mL/mL or less.

According to a certain one embodiment of the second aspect of thepresent invention, the porosity of the above-mentioned inorganic poroussubstance may be 50% or more.

According to a certain one embodiment of the second aspect of thepresent invention, a density of the above-mentioned grafted linker maybe within a range of 0.1 μmol/m² or more to 5.0 μmol/m² or less relativeto a specific surface area per mass of the inorganic porous substance.

According to a certain one embodiment of the second aspect of thepresent invention, a particle diameter (a median diameter) of theinorganic porous substance may be within a range of 1 μm or more to 1000μm or less. According to a certain one embodiment of the second aspectof the present invention, the inorganic porous substance may be silica,silica gel, zeolite, or glass.

In the third aspect of the present invention, a method for preparing anucleic acid is provided, which is carried out using the inorganicporous carrier wherein R_(b) in the general formula (2) represents anucleoside or nucleotide in which a hydroxyl group as a reactive groupis protected, wherein the method comprises the following steps:

a step (A) of deprotecting a protecting group of the hydroxyl group at a5′position of the nucleoside;

a step (B) of subjecting the hydroxyl group at the 5′position of thenucleoside produced in the step (A) to a condensation reaction with anamidite compound having a second nucleoside base to produce a phosphite;

a step (C) of oxidizing the phosphite produced in the step (B) toproduce a nucleotide; and

a step (D) of deprotecting a protecting group of a hydroxyl group at a5′position of the nucleotide produced in the step (C).

In one embodiment according to the third aspect of the presentinvention, the method for preparing nucleic acid may further comprisethe following steps:

a step (B′) of subjecting the product produced in the step (D) to acondensation reaction with an amidite compound having a nucleoside baseto be introduced in next time to produce a phosphite;

a step (C′) of oxidizing the phosphite produced in the step (B′) toproduce an oligonucleotide; and

a step (D′) of deprotecting a protecting group of a hydroxyl group at a5′position in an end of an oligonucleotide strand produced in the step(C′).

In one embodiment according to the third aspect of the presentinvention, the method for preparing nucleic acid may further comprise astep (E) of carrying out a series of steps consisting of the above step(B′), step (C′) and step (D′) repeatedly m times (wherein m is aninteger of 1 or more) to react the number of m of amidite compounds, andthen cleaving an elongated nucleic acid.

In the fourth aspect of the present invention, it is provided a use ofthe inorganic porous carrier according to the first aspect or asolid-phase carrier according to the second aspect in a preparation of anucleic acid by a phosphoramidite method.

Effect of Invention

The inorganic porous carrier according to the present invention canfurther improve the purity of nucleic acid in the preparation of nucleicacid.

The method for preparing nucleic acid according to the present inventioncan further improve the purity of nucleic acid, and particularly obtaina long-strand nucleic acid in high yield.

MODE FOR CARRYING OUT THE INVENTION

As used herein, when a certain numerical range is referred to as “A toB” or “A-B”, it means a range represented by “from A or more to B orless” unless otherwise stated.

(Inorganic Porous Carrier)

The inorganic porous carrier of the first aspect of the presentinvention is explained.

<Inorganic Porous Substance>

The inorganic porous substance constituting the inorganic porous carrierof the present embodiment is an inorganic porous substance wherein amode diameter in a pore distribution as measured by mercury intrusionmethod is 0.04 μm to 1 μm, and also a cumulative pore volume ratio ofcumulative pore volume (VB) whose pore size being within a range of0.004 μm to 0.04 μm relative to cumulative pore volume (VA) whose poresize being within a range of 0.04 μm to 1 μm is 30% or less.

The inorganic porous substance has typically a silanol group that cansupport a silane coupling agent. As a typical examples of the inorganicporous substance, silica, silica gel, zeolite, glass, or quartz isexemplified, preferably silica, silica gel, zeolite or glass isexemplified. These compounds may be used as a commercially availableproduct, or may be used as one obtained by preparing according to thebelow-mentioned synthesis method.

[Method for Preparing Inorganic Porous Substance Containing SilanolGroup]

Examples of the method for preparing the inorganic porous substancecontaining the silanol group include a dry method and a wet method.Specific examples of the former include a combustion method and an arcmethod, and specific examples of the latter include synthesis methodssuch as a precipitation method, a sol-gel method, and a hydrothermalsynthesis method (Reference: TOSOH Research & Technology Review Vol. 45(2001).).

The preparation of such an inorganic porous substance is carried out by,for example, using silicate, alkoxysilane, chlorosilanes or the like asraw materials according to the synthesis method as described above usinga solvent and a template.

The preparation of the inorganic porous substance can be carried out,for example, according to any one of the following methods: 1. a methodof precipitating silica, and then removing a solvent contained in aframework of the silica; 2. a method of precipitating a solid aftermixing silica with dissimilar metal other than silica such as aluminum,boron, or the like, and then phase-separating the resulting mixture intoa silica component and a component other than silica, and removing thecomponent other than silica; 3. a method of precipitating silica aftermixing silica with an ammonium salt or a polymer as a template agent,and then removing the template agent; and 4. a method of aggregating aprecipitated silica. A combination of two or more of the above methodsmay be used.

The methods of removing the solvent or the template agent in the abovemethods 1 and 3 may include drying, supercritical extraction, calciningor the like.

As silica which is aggregated by the method 4, silica, silica gel,zeolite, glass or quartz, or two or more thereof may be used.

The zeolite is a substance containing silicon and oxygen as an elementcomposed of the framework of the zeolite, and may be crystalline silicawhose framework is substantially composed of silicon and oxygen, and maybe crystalline metallosilicates and so on further containing otherelements as a constitute element for the framework.

In the case of metallosilicate and so on, examples of the elements thatmay be existed as the element other than silicon and oxygen includeanyone kind of the followings selected from Be, B, Al, Ti, V, Cr, Fe,Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Sb, La, Hf or Bi, and as needed, two ormore kinds of these elements may be contained.

Also, the atomic ratio of silicon against existing elements other thansilicon and oxygen is preferably 5 or more, and further preferably 500or more.

The above-mentioned zeolites may be synthesized by a hydrothermalsynthesis of a mixture containing silicon compound, water and quaternaryammonium hydroxide.

Examples of the above-mentioned silicon compound include amorphoussilica; alkaline silicates such as sodium silicate and potassiumsilicate; tetraalkyl orthosilicate such as tetramethyl orthosilicate,tetraethyl orthosilicate, tetrapropyl orthosilicate, and tetrabutylorthosilicate, and as needed, two or more kinds of these compounds canbe used.

Examples of the above-mentioned quaternary ammonium hydroxide preferablyinclude tetraalkyl ammonium hydroxides. Examples of the tetraalkylammonium hydroxide include for example, tetramethyl ammonium hydroxide,tetraethyl ammonium hydroxide, n-propyl trimethyl ammonium hydroxide,tetra-n-propyl ammonium hydroxide, tetra-n-butyl ammonium hydroxide,triethyl methyl ammonium hydroxide, tri-n-propyl methyl ammoniumhydroxide, and tri-n-butyl methyl ammonium hydroxide, or two or morekinds of these compounds.

The molar ratio of water relative to silicon in the mixture of thehydration synthesis is within a range of 5 to 100, more preferably 10 to60.

The molar ratio of the quaternary ammonium ion relative to silicon inthe mixture is preferably 0.1 to 0.6, and more preferably 0.2 to 0.5.

The molar ratio of the hydroxide ion relative to silicon in the mixtureto be subjected to a hydration synthesis is adjusted to usually 0.1 to0.6, preferably 0.2 to 0.5. As the molar ratio of the hydroxide ionrelative to the silicon in the mixture is higher, the primary particlediameter of the obtained zeolite has a tendency to become small.

The molar ratio of potassium relative to the silicon in the mixture isadjusted to preferably 0 to 0.1, more preferably 0.04 to 0.1. The molarratio of potassium relative to the silicon in the mixture can beadjusted appropriately, for example, by adjusting a used amount of thesilicon compound, or adjusting the content of each rough material,particularly, potassium compound which may be contained as impurematerial in the quaternary ammonium hydroxide.

When the mixture is subjected to a hydration synthesis reaction, thetemperature of the hydration synthesis is preferably 80 to 160° C., morepreferably 100 to 140° C. The duration of the hydration synthesis ispreferably 1 to 200 hours, more preferably 12 to 72 hours. The pressureof the hydration synthesis is preferably within a range of 0.10 to 1.0MPa as an absolute pressure, more preferably 0.11 to 0.50 MPa.

The method for hydration synthesis is not particularly limited, and, forexample, can be carried out by enclosing the above-mentioned mixtureinto a reactor such as autoclave and then subjecting the resultingmixture to the reaction in a sealed state under the above-mentionedtemperature condition while stirring.

The inorganic porous substance which is obtained by any one of themethod of 1. to 4. in the above-mentioned preparation for inorganicporous substance or two or more thereof in combination is preferably ina form of particles, and may be formed into a spherical shape, or may beformed into a massive shape or a crushed shape, whereas, when they areused as carriers, the spherical shape or the crushed shape is preferablefrom the viewpoint of filling into a column for nucleic acid synthesis.The molding method is not particularly limited, but a spray dryingmethod or an emulsion method may be used.

In this embodiment, a cumulative pore volume ratio (%) represents avalue calculated by the following equation.

Cumulative  Pore  Volume  Ratio(%) = V B/VA × 100

[Mercury Intrusion Method]

A pore diameter of an inorganic porous substance can be determined asfollows.

First, a container containing a sample is evacuated in vacuum and thecontainer is filled with mercury. A mercury has a high surface tension,and a mercury does not infiltrate into a pore of surface of the samplein situ (normal pressure), however, as a pressure applies to mercury anda pressure is increased gradually, a mercury is infiltrating graduallyinto a pore from a pore having a large diameter to a pore having a smallpore. By measuring a press-fitting amount f mercury into a pore while apressure is being increased continuously, a curve of mercurypress-fitting curve is obtained from a correlation between a pressureapplied to mercury and a press-fitting amount of mercury.

Here assuming that a shape f a pore is a cylindrical, when a pressureapplied to a mercury is expressed as P, its pore size (pore diameter) isexpressed a D, a surface tension of mercury is expressed as σ, a contactangle between a mercury and a sample is expressed as θ, a pore size(pore diameter) is expressed as the following equation (A).

$\begin{matrix}{{D = \text{?}}{\text{?}\text{indicates text missing or illegible when filed}}} & (A)\end{matrix}$

In general, a surface tension of mercury σ uses a value of 0.48 to 0.49N/m, and a contact angle θ uses 13- to 140°.

Since σ and θ are both a constant value, a correlation between apressure applied to mercury: P and a pore diameter: D can be determinedby an equation A. By measuring an infiltrate volume of mercury at thatmoment, a pore volume can be calculated. That is, since there iscorrelation between the pressure applied to mercury: P and the porediameter infiltrated by mercury: D, a pore distribution curve, whichindicates a correlation between a size and a volume with respect to apore diameter of the sample, can be obtained based on a curve of mercurypress-fitting curve.

Here an approximate measurement limit of the pore diameter by a memoryintrusion method is set to be about 0.004 μm or less as a lower limitand about 200 μm as an upper limit. A measurement by a mercury intrusionmethod can be carried out with a device such as a mercury porosimeter.Specific examples of the mercury porosimeter include AutoPoreIV9520(manufactured by Micromeritics).

The inorganic porous substance according to this embodiment has a mostfrequent value (a mode diameter) of a pore size of 0.04 μm to 1 μm,preferably 0.04 μm to 0.5 μm, more preferably 0.04 μm to 0.3 μm in apore distribution determined by a mercury intrusion method.

When the mode diameter is the lower limit value or more which isincluded within the above range, a steric hindrance between oligonucleicacids in a pore is unlikely to occur during the nucleic acid elongationreaction, the elongation reaction can easily proceed stably to achievethe target chain length. Whilst, when the mode diameter is the upperlimit value or less which is included within the above range, it is easyto keep the surface area as a carrier which is sufficient for obtainingoligonucleic acid.

The mode diameter represents a pore size determined from a value ofX-axis at a peak top in the pore size distribution obtained by themercury intrusion method (a graph in which the X-axis is a value of thepore size and the Y-axis is a value obtained by differentiating the porevolume by the pore size).

Also, in the inorganic porous substance according to this embodiment, acumulative pore volume ratio of cumulative pore volume (VB) whose poresize being within a range of 0.004 μm to 0.04 μm relative to cumulativepore volume (VA) whose pore size being within a range of 0.04 μm to 1 μmis 30% or less, preferably 26% or less, and more preferably % or less.The lower the lower limit value of the cumulative pore volume ratio is,it becomes more preferable, and it is substantially 3% or more, forexample.

When the cumulative pore volume ratio is the upper limit value or lesswhich is included within the above range, that is, 30% or less, thehomogeneity of the pore size is increased, and as a result, it becomeseasier to obtain a nucleic acid having a target strand length, and canachieve a high purity.

A size of the inorganic porous substance is not particularly limited,but from the viewpoint of column filling efficiency in the solid-phasesynthesis of nucleic acid, and liquid feeding rate in a column filling,and the like, a particle size (median diameter, the same shall applyhereinafter) which is measured by a laser diffraction method (scatteringmethod) is preferably within a range of 1 to 1000 μm, more preferably 5to 500 μm, and further more preferably 10 to 300 μm.

The pore volume of the inorganic porous substance of the presentembodiment is not particularly limited. Generally, in order to improvethe productivity of nucleic acid per column, it is preferable that thepore volume per volume of the inorganic porous substance (mL/mL) is highregardless of the strand length of the nucleic acid. The pore volume pervolume of the inorganic porous substance is preferably within a range of0.05 to 0.6 mL/mL, and more preferably 0.05 to 0.5 mL/mL.

The pore volume per volume of the inorganic porous substance isdetermined by multiplying the bulk density (g/mL), which is measured bythe mercury intrusion method, by the cumulative pore volume (VA) (mL/g)of pore having a pore size within a range of 0.04 μm to 1 μm.

A porous substance having a pore size of 0.04 μm or more is used as theinorganic porous substance. The inorganic porous substance to be usedcan be appropriately selected depending on the strand length of thenucleic acid to be synthesized. In general, when a strand length of thenucleic acid to be synthesized becomes long, it is preferable to selectthe inorganic porous substance having a large pore size. For example,when RNA of 40-mer to 200-mer is synthesized, the pore size ispreferably within a range of 0.04 μm or more and 0.5 μm or less, andmore preferably within a range of 0.04 μm or more and 0.3 μm or less.

The pore size (mode diameter) is determined based on a value of X-axisat a peak top in the pore size distribution obtained by the mercuryintrusion method (a graph in which the X-axis is a value of the poresize and the Y-axis is a value obtained by calculating differentiallythe pore volume by the pore size).

The porosity of the inorganic porous substance is not particularlylimited, and generally, in order to improve the productivity of nucleicacid per column, it is preferable that the porosity is high regardlessof the strand length of the nucleic acid. The porosity is determined bythe mercury intrusion method, and it is preferably 50% or more, and morepreferably 70% or more.

The porosity herein is calculated based on the pore volume of porehaving a pore size within a range of 0.004 to 200 μm, which is a rangemeasured by the mercury intrusion method. That is, it is determined bymultiplying the cumulative pore volume (mL/g) of pore having a pore sizewithin the range of 0.004 μm to 200 μm by the bulk density (g/mL).

The inorganic porous carrier of the present embodiment contains a linkerrepresented by the following general formula (1):

[wherein,

a bond marked with * represents a linkage to the oxygen atom of asilanol group in an inorganic porous substance;

n is an integer of 1, 2 or 3;

R represents independently of each other an alkyl group containing 3 to10 carbon atoms which may optionally have a substituent selected from analkoxy group and a fluorine atom; a phenyl group which may optionallyhave a substituent selected from an alkyl group, an alkoxy group, and afluorine atom; a hydroxyl group; or an alkoxy group containing 1 to 4carbon atom; and

L represents a single bond; an alkylene group of 1 to 20 carbon atoms;or an alkylene group containing 2 to 20 carbon atoms which contains—CH₂-Q-CH₂— group wherein any group Q selected from a group consistingof —O—, —NH—, —NH—CO— and —NH—CO—NH— is inserted into at least one of—CH₂—CH₂— group constituting the alkylene group; providing that a carbonatom of the methylene group bound to the group Q does not bind toanother group Q at the same time].

In the formula (1), the alkyl group in each of R may be any of a linearalkyl group, a branched alkyl group or a cyclic alkyl group, andpreferably a branched alkyl group so as to improve the yield easily. Thealkyl group in each of R¹ and R² contains 3 to 10 carbon atoms,preferably 3 to 6 carbon atoms, and more preferably 3 or 4 carbon atoms.

Examples of the alkyl group in each of R include a linear alkyl groupsuch as n-propyl group, n-butyl group, n-hexyl group and n-octyl group;a branched alkyl group such as isopropyl group, isobutyl group,sec-butyl group, tert-butyl group, 2-ethylhexyl group and3,7-dimethyloctyl group; and a cyclic alkyl group such as cyclopropylgroup and cyclohexyl group.

The substituent which may be optionally substituted on the alkyl grouprepresented by each of R is an alkoxy group or a fluorine atom. Examplesof the alkoxy group include an alkoxy group containing 1 to 3 carbonatoms.

The substituent which may be optionally substituted on the phenyl grouprepresented by each of R is an alkyl group, an alkoxy group, or afluorine atom. Examples of the alkyl group include an alkyl groupcontaining 1 to 5 carbon atoms. Examples of the alkoxy group include analkoxy group containing 1 to 3 carbon atoms.

In the case where n is 1 in the formula (1), a plural of R may beidentical to or different from each other, and preferably identical toeach other from the viewpoint of synthesis (for example, convenience andefficiency).

In the above-mentioned formula (1), an alkoxy group as R represents analkoxy group containing 1 to 4 carbon atoms, preferably an alkoxy groupcontaining 1 to 3 carbon atoms, and more preferably a methoxy group oran ethoxy group.

In the formula (1), the alkylene group in L may be any of a linearalkylene group or a branched alkylene group, and preferably a linearalkylene group so as to improve the yield easily. The alkylene group inL contains 1 to 20 carbon atoms, preferably 1 to 10 carbon atoms, andmore preferably 1 to 6 carbon atoms.

Also an alkylene group as L may represent an alkylene group containing 2to 20 carbon atoms which contains —CH₂-Q-CH₂— group wherein any group Qselected from a group consisting of —O—, —NH—, —NH—CO— and —NH—CO—NH— isinserted into at least one of —CH₂—CH₂— group constituting the alkylenegroup.

With the proviso that in this embodiment, in the linker represented bythe above-mentioned general formula (1), a carbon atom of the methylenegroup bound to the group Q does not bond to another group Q at the sametime.

As examples of the inorganic porous carrier, for example, any one of thefollowing linkers represented by formulae (1-1), (1-2) or (1-3) or aplural forms selected from these linkers are exemplified.

In the above-mentioned formula (1-1), (1-2) and (1-3), *, R and L havethe same meanings as those of *, R and L as described in theabove-mentioned formula (3).

The inorganic porous carrier of the present embodiment can be prepared,for example, by a method of treating a surface of the inorganic poroussubstance with a silane coupling agent represented by the followinggeneral formula (3).

[wherein,

n is an integer of 1, 2 or 3;

R represents independently of each other an alkyl group containing 3 to10 carbon atoms which may optionally have a substituent selected from analkoxy group and a fluorine atom; a phenyl group which may optionallyhave a substituent selected from an alkyl group, an alkoxy group, and afluorine atom; a hydroxyl group; or an alkoxy group containing 1 to 4carbon atom;

R¹ represents independently of each other a hydrogen atom or al alkylgroup;

L represents a single bond; an alkylene group of 1 to 20 carbon atoms;or an alkylene group containing 2 to 20 carbon atoms which contains—CH₂-Q-CH₂— group wherein any group Q selected from a group consistingof —O—, —NH—, —NH—CO— and —NH—CO—NH— is inserted into at least one of—CH₂—CH₂— group constituting the alkylene group; providing that a carbonatom of the methylene group bound to the group Q does not bind toanother group Q at the same time].

In the above-mentioned formula (3), R and L have the same meanings asthose of R and L as described in the above-mentioned formula (1).

The preparation of the inorganic porous carrier containing the linkerrepresented by the general formula (1) is carried out, for example, by amethod of mixing the inorganic porous substance with a certain silanecoupling agent and a solvent, and then removing the solvent. In thiscase, the certain silane coupling agent is covalently bound to a silanolgroup on the surface of the inorganic porous substance by the mixing toform an inorganic porous carrier supporting the linker represented bythe general formula (1).

Examples of the solvent as described above include acetonitrile,toluene, anisole, 2-heptanone, propyleneglycol monomethyl ether acetate,N,N-dimethylformamide, tetrahydrofuran, pentane, hexane, heptane,xylene, mesitylene, dichloromethane, chlorobenzene, water and the like,or a mixture of two or more thereof, and preferably include toluene.

The above-mentioned inorganic porous substance and solvent arepreferably used after being dehydrated from the viewpoint of suppressinga polymerization of the silane coupling agent as itself and facilitatingthe reaction of the silane coupling agent with the surface of theinorganic porous substance. The dehydration method is not particularlylimited, but examples thereof include a method of heating the inorganicporous substance under reduced pressure; and a method of dispersing theinorganic porous substance in the solvent and then distilling off thesolvent under normal pressure or reduced pressure to conduct anazeotrope dehydration.

When the inorganic porous substance is mixed with the silane couplingagent and the solvent, the mixture is usually heated to near the boilingpoint of the solvent to facilitate the reaction, but the temperature isnot limited thereto, and the mixture may be mixed at room temperature,or in a state where it is cooled to room temperature or less.

The reaction of the inorganic porous substance with the silane couplingagent is usually carried out for about 1 to 12 hours, but in the casethat the silane coupling agent containing an amino group is used, sincethe silane coupling agent as itself has a catalytic effect offacilitating the reaction, the reaction may be carried out for about aseveral minutes.

The amount of the silane coupling agent to be added is usually an amountin which a density of the grafted linker is within a range of 0.1 to 5.0μmol/m², and preferably 0.5 to 2.0 μmol/m², relative to the specificsurface area per mass of the inorganic porous substance, which isdetermined by N₂ adsorption/desorption measurement.

The silanol group which is not used in the reaction with the silanecoupling agent, if needed, may be capped with a functional group whichis inert to the nucleic acid synthesis, for example, trimethylsilylgroup.

As described above, the surface of the inorganic porous substance can betreated with a certain silane coupling agent to produce the inorganicporous carrier which is modified with an aminosilyl group.

The silane coupling agent represented by the above general formula (3)can be prepared through the reaction route as shown below (syntheticroute 1, synthetic route 2, or synthetic route 3).

Details of synthetic route 1 (Compound 1→Compound 2→Compound 3→Compound6):

For example, when compound 1 is trichlorosilane, the compound 1 isreacted with an organolithium compound or an organomagnesium compoundcorresponding to R (nucleophilic substitution reaction) to obtaincompound 2 (Step 1). Then, the compound 2 is reacted with R¹OH (forexample, methanol, ethanol, propanol, etc.) in the presence of a base,or is reacted with an alcoholate such as R¹ONa or water (R¹: hydrogen)to obtain silane compound 3 (Step 2). Then, the compound 3 is subjectedto a hydrosilylation reaction with an amine compound or a halogencompound containing a terminal olefin (for example, allylamine or6-chloro-1-hexene) in the presence of a platinum catalyst to synthesizesilane compound (Step 3). Alternatively, when compound 1 is analkoxysilane (for example, trimethoxysilane, triethoxysilane, etc.),substituents (R) may be introduced into the compound 1 by a nucleophilicsubstitution reaction according to the same reaction as described above,and then the resulting compound may be subjected to the hydrosilylationreaction to synthesize the silane compound 6.

Details of synthetic route 2 (Compound 1→Compound 5→Compound 7→Compound6):

For example, when compound 1 is trichlorosilane, the compound 1 issubjected to a hydrosilylation reaction with a compound 4 (wherein Yrepresents a halogen atom, and m is an integer of 1 to 18) in thepresence of a platinum catalyst, and accordingly a strand providing aspacer is attached thereto to obtain compound 5. Then, the substituents(R) are introduced thereto by a nucleophilic substitution reactionaccording to the above similar reaction to obtain compound 7. Then, thecompound 7 is reacted with RICH (for example, methanol, ethanol,propanol, etc.) in the presence of a base, or is reacted with analcoholate such as R¹ONa or water (R¹: hydrogen) to obtain the silanecompound 6 (Lg: R¹O group).

The introduction of R¹O group (methoxy group, ethoxy group, propoxygroup, etc.) can be carried out by a method of adding methanol, ethanol,propanol, or the like as the reagent to a solution containing thecompound 2 (Lg: halogen atom) or the compound 4 (Lg: halogen atom); or amethod of adding the compound 2 or the compound 6 dropwise to thecorresponding alcohol or a solution containing the correspondingalcohol.

Details of synthetic route 3 (Synthetic route for Compound 6→silanecoupling agent):

In the above-mentioned synthetic route 1 and synthetic route 2, thesilane compound 6 which contains a functional group Y (an amino group ora halogen atom) may be obtained.

When the functional group Y is an amino group, various silane couplingagents can be prepared by a method of carbamoylation, amidation orureidation of the amino group of the silane compound 6.

When the functional group Y is a halogen atom, the silane compound 6 isreacted with an ammonia or a primary amine compound, and accordingly thehalogen atom is eliminated, and an amino group or an imino group (—NH—)is introduced thereto or an ether bond is introduced thereto, to obtainvarious silane coupling agent.

It is preferable to use a reaction solvent in any of the above-mentionedreactions. The reaction solvent is preferably an organic solvent such aspentane, hexane, heptane, toluene, tetrahydrofuran, or the like, or amixture of two or more thereof.

The silane compound is usually purified by distillation under normalpressure or reduced pressure conditions. The obtained silane couplingagent is purified by, for example, liquid separation, distillation, orcolumn chromatography.

(Method for Preparing Nucleic Acid)

In the method for preparing nucleic acid of the present embodiment, thenucleic acid can be synthesized with the above-mentioned inorganicporous carrier according to a publicly known method. Particularly, thepreparation of nucleic acid is preferably carried out according to thephosphoramidite method. The nucleic acid synthesis method according tothe phosphoramidite method is described below.

[Preparation of Solid-Phase Carrier]

A solid-phase carrier refers to a carrier wherein a nucleoside, ornucleotide in which a reactive group is protected or deprotected isbound to the amino group (—NH₂) contained in the above-mentionedinorganic porous carrier through a divalent group.

In this embodiment, an inorganic porous carrier that comprises a linkerrepresented by general formula (2) wherein a mode diameter in a poredistribution as measured by mercury intrusion method is 0.04 μm to 1 μm,and also a cumulative pore volume ratio of cumulative pore volume (VB)whose pore size being within a range of 0.004 μm to 0.04 μm relative tocumulative pore volume (VA) whose pore size being within a range of 0.04μm to 1 μm is 30% or less can be used as a solid-phase carrier.

[wherein

a bond marked with * represents a linkage to the oxygen atom of asilanol group in an inorganic porous substance;

n is an integer of 1, 2 or 3;

R represents independently of each other an alkyl group containing 3 to10 carbon atoms which may optionally have a substituent selected from analkoxy group and a fluorine atom; a phenyl group which may optionallyhave a substituent selected from an alkyl group, an alkoxy group, and afluorine atom; a hydroxyl group; or an alkoxy group containing 1 to 4carbon atom;

L represents a single bond; an alkylene group containing 1 to 20 carbonatoms; or an alkylene group containing 2 to 20 carbon atoms whichcontains —CH₂-Q-CH₂— group wherein any group Q selected from the groupconsisting of —O—, —NH—, —NH—CO—, and —NH—CO—NH— is inserted into atleast one —CH₂—CH₂— group constituting the alkylene group; providingthat a carbon atom of the methylene group bound to the group Q doses notbind to another group Q at the same time;

R_(b) represents a nucleotide or a nucleotide in which a reactive groupis protected or deprotected; and

L₁ represents a divalent group bound to an oxygen atom of a primary or asecondary hydroxy group as R_(b).].

In the formula (2), R and L are described in the same manner as thedescription of R and L in the formula (1).

In the formula (2), the divalent group L₁ bound to the imino group(—NH—) preferably contains a succinyl group as a functional group.

Examples of the divalent group L₁ typically include a succinyl linker, auniversal linker, and a linking group which is composed of a universallinker and a group linking an imino group (—NH—) in the formula (2) tothe universal linker.

The universal linker contains a functional group (typically, a hydroxylgroup) which can form a phosphite with the hydroxyl group of thenucleotide that provides a starting point of nucleic acid synthesis, anda functional group which can bond to an amino group at the end of linkerrepresented by the formula (1), and further contains an adjacentprotected functional group (for example, a protected amino group, aprotected hydroxyl group, or a protected thiol group) in the samemolecule, which can nucleophilically attack a phosphorus atom ofphosphoric acid under the conditions for cleaving the synthesizednucleic acid.

More specifically, examples of the divalent group L₁ include a linkinggroup represented by the following formula L₁₀, and a linking grouprepresented by the following formula L₁₁.

Here, in each of the formulae L₁₀ and L₁₁, the bond marked with

represents a bond to the imino group (—NH—) in the formula (2). The bondmarked with # represents a bond to an oxygen atom of a primary orsecondary hydroxyl group of R_(b) in the above formula (2).

In the formula L₁₁, Z₁ represents a protected amino group, a protectedhydroxyl group, or a protected thiol group. The oxygen atom and Z₁ whichare bound to Z represent groups which are adjacent to each other (forexample, they exist in vicinal position, and carbon atoms of Z that areattached thereto are directly bound to each other).

L₁₂ represents a group which links the imino group (—NH—) to theuniversal linker (for example, represented by e

-CO(CH₂)₂CO—&; and

the bond marked with & represents a bond to Z).

When the universal linker is used, even though the 3′end of the nucleicacid to be synthesized becomes any kinds of nucleoside or nucleotide,the nucleoside phosphoramidide providing the 3′end can be reacted andintroduced in the same manner as the method of elongating the nucleicacid according to the usual nucleic acid automatic synthesis. Examplesof such a universal linker include the compounds described in thefollowing references, but are not limited thereto:

REFERENCE

-   A. P. Guzaev, and M. Manoharan, J AmChem Soc, 2003, 125, 2380-2381.

REFERENCE

-   R. K. Kumar, A. P. Guzaev, C. Rentel, and V. T. Ravikumar,    Tetrahedron, 2006, 62, 4528.

In the formula (2), it is preferable for R_(b) that the hydroxyl groupat the 5′position of the nucleoside, which provides the starting pointof the nucleic acid elongation reaction, is protected with atrityl-based protecting group (for example, 4,4′-dimethoxytrityl (DMTr)group, etc.).

Similarly, when the universal linker is used, it is preferable that thehydroxyl group, which provides the starting point of the nucleic acidelongation reaction, is protected with a trityl-based protecting group(for example, 4,4′-dimethoxytrityl (DMTr) group, etc.).

The solid-phase carrier containing the linker represented by the formula(2) is typically prepared by a condensation reaction of the inorganicporous carrier containing the linker represented by the general formula(1) with the compound (R_(b)-L₁₀-W). This L₁₀ represents a linking grouprepresented by the above-mentioned formula L₁₀. W represents a reactivefunctional group (for example, a hydroxyl group).

When the nucleoside linker is used, the nucleoside linker correspondingto the base at the 3′end is selected depending on the sequence of RNA tobe synthesized. Examples of the nucleoside linker include a nucleosidelinker containing a succinyl group as a functional group to be reactedwith an amino group (—NH₂).

Examples of the nucleoside linker containing a succinyl group are shownbelow.

In the following formulae, each of marks * represents a bond to theimino group (—NH—) in the above-mentioned formula (2). TBDMS refers to atert-butyldimethylsilyl group. Ac refers to an acetyl group.

The condensation reaction as described above is carried out by mixingthe inorganic porous carrier, the compound (R_(b)-L₁₀-W), the condensingagent and an appropriate solvent, and usually shaking the mixture atroom temperature or heating the mixture to facilitate the condensationreaction. The condensation reaction may ales be carried out by allowingthe mixture to stand without shaking and with stirring.

As the condensing agent for the condensation reaction, any condensingagent to be usually used for an amide condensation can be used. Specificexamples of the condensing agent include N,N′-dicyclohexylcarbodiimide(DCC), N,N′-diisopropylcarbodiimide (DIC),1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDAC),1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC),1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium3-oxide hexafluorophosphate (HATU),1-[bis(dimethylamino)methylene]-1H-1,2,3-benzotriazolium 3-oxidehexafluorophosphate (HBTU),1-[bis(dimethylamino)methylene)]-1H-1,2,3-triazolo[4,5-b]pyridinium3-oxide tetrafluoroborate (TATU),1-[bis(dimethylamino)methylene]-1H-1,2,3-benzotriazolium 3-oxidetetrafluoroborate (TBTU),(1-cyano-2-ethoxy-2-oxoethylideneaminooxy)dimethylaminomorpholinocarbeniumhexafluorophosphate (COMU),0-[(ethoxycarbonyl)cyanomethyleneamino]-N,N,N′,N′-tetramethyluroniumhexafluorophosphate (TOTU) and the like, or a mixture of two or morethereof. Additives such as N,N-dimethyl-4-aminopyridine (DMAP) andN,N-diisopropylethylamine may be added.

The solid-phase carrier after the completion of the condensationreaction is filtered by filtration with a solvent, and collected.Examples of the solvent for filtration include acetonitrile and thelike. Capping treatment to the unreacted amino group may be carried out.Examples of the capping treatment agent to be used include aceticanhydride (for example, acetic anhydride-tetrahydrofuran solution) andphenoxyacetic anhydride (for example, phenoxyacetic anhydride/N-methylimidazole solution). The success or failure of capping can be confirmedby a ninhydrin test. When a nucleoside linker or universal linker havinga protecting group such as 4,4′-dimethoxytrityl (DMTr) group is used,the quantification of the reacted nucleoside can be carried out bycleaving the DMTr group with an acid and then measuring an absorbancethereof.

The amount of (R_(b)−L₁) supported is usually within a range of 0.1 to5.0 μmol/m², and preferably 0.5 to 2.0 μmol/m², relative to the specificsurface area per mass of the inorganic porous substance, which isdetermined by N₂ adsorption/desorption measurement.

The solid-phase carrier of the present embodiment is preferable as asubstrate for a solid-phase synthesis of nucleic acid (DNA and RNA).Further, the solid-phase carrier of the present embodiment isparticularly suitable for the synthesis of RNA, which has beenconsidered to have a problem in stability as compared with DNA.

Hereinafter, the solid-phase synthesis of RNA is illustrated as anexample of the preparation method, and the method for preparing nucleicacid is described with reference to a reaction route shown below(condensation reaction, oxidation, and deprotection).

Here, relative to the reaction route illustrated below, an example inwhich a nucleoside is used as R_(b) in the formula (2) is shown.

In the chemical formula shown in the above reaction route, R⁶ representsa base; Tr represents a protecting group; and X represents —H, —OH or—OR⁷ (wherein, R⁷ represents a protecting group).

The base (R⁶) constituting the nucleoside of the solid-phase carrier(Sp-Nu) containing the linker represented by the general formula (2) andthe nucleoside of the amidite monomer (Am-1) is usually a nucleic acid,and typically a naturally-occurring base which is composed of RNA,however, may be a non-naturally-occurring base in some cases. Examplesof such the non-naturally-occurring base include modified analogs of thenaturally-occurring base or non-naturally-occurring base.

Examples of the base represented by R⁶ include purine bases such asadenine, isoguanine, xanthine, hypoxanthine and guanine; and pyrimidinebases such as cytosine, uracil and thymine; and the like.

Examples of the base represented by R⁶ further include amino derivativessuch as 2-aminoadenine, 2-aminopurine, and 2,6-diaminopurine; alkylderivatives such as 5-methyluracil, 5-methylcytosine, 7-methylguanine,6-methylpurine, 2-propylpurine; 5-halouracil and 5-halocytosine;5-propynyluracil and 5-propynylcytosine; 6-azauracil, 6-azacytosine and6-azathymine; 5-uracil (pseudouracil), 4-aminoallyluracil; 8-substitutedpurines, for example, 8-halogenated, aminated, thiolated, thioalkylatedor hydroxylated purine, or other 8-substituted purine; 5-substitutedpyrimidines, for example, 5-trifluoromethylated pyrimidine, or other5-substituted pyrimidine; 6-azapyrimidine; N-2, N-6 or 0-6 substitutedpurines (including 2-aminopropyladenine); dihydrouracil;3-deaza-5-azacytosine; 7-deazaadenine; N6-methyladenine,N6,N6-dimethyladenine; 5-amino-allyl-uracil; N3-methyluracil;substituted 1,2,4-triazole; 2-pyridinone; 5-nitroindole; 3-nitropyrrole;5-methoxyuracil; uracil-5-oxyacetic acid; 5-methoxycarbonylmethyluracil;2-thiouracil, 5-methyl-2-thiouracil;5-methoxycarbonylmethyl-2-thiouracil; 5-methylaminomethyl-2-thiouracil,3-(3-amino-3-carboxypropyl)uracil; 3-methylcytosine; N4-acetylcytosine;2-thiocytosine; N6-methyladenine; N6-isopentyladenine;2-methylthio-N6-isopentenyladenine; N-methylguanine; O-alkylated bases,or the like; and a mixture of two or more thereof.

Further, examples of purine compounds and pyrimidine compounds includethose disclosed in each of U.S. Pat. No. 3,687,808; “ConciseEncyclopedia Of Polymer Science And Engineering, pp. 858-859, edited byKroschwitz J. I., John Wiley & Sons, 1990; and Englisch et al.,Angewandte Chemie, International Edition, 1991, vol. 30, p. 613.

Examples of the amidite monomer (Am-1) preferably include TBDMS amidite(TBDMS RNA Amidites, product name, ChemGenes Corporation), ACE amidite,TOM amidite, CEE amidite, CEM amidite, TEM amidite (Reviews byChakhmakhcheva: Protective Groups in the Chemical Synthesis ofOligoribonucleotides, Russian Journal of Bioorganic Chemistry, 2013,Vol. 39, No. 1, pp. 1-21.), and EMM amidite (as described inWO2013/027843 A1), or the like, in which the protecting group R⁷ in thecompound represented by the following chemical formula (Am-1′) istert-butyldimethylsilyl (TBDMS) group, bis(2-acetoxy)methyl (ACE) group,(triisopropylsilyloxy)methyl (TOM) group, (2-cyanoethoxy)ethyl (CEE)group, (2-cyanoethoxy)methyl (CEM) group, para-tolylsulfonylethoxymethyl(TEM) group, (2-cyanoethoxy)methoxymethyl (EMM) group, or the like.

[wherein, R⁷ represents a protecting group of the hydroxyl group; and R⁶represents a protected nucleobase.]

The solid-phase carrier of the present embodiment may also be used toincorporate a divalent group other than a nucleoside and nucleotide intoa nucleic acid sequence. For example, an amidite having a prolineframework (for example, Amidite P as described later) can beincorporated into a nucleic acid sequence according to the amiditemethod (see the same method as the method of Example A4 of WO2012/017919A1). Further, the amidite represented by each of the followingstructural formulae (Am-11). (Am-12) and (Am-13) (see Examples A1 to A3of WO2013/103146 A1) may also be used.

[wherein, iPr represents an isopropyl group, DMTr represents a4,4′-dimethoxytrityl group, and Tfa represents a trifluoroacetyl group.]

[Solid-Phase Synthesis of RNA]

The solid-phase carrier (Sp-Nu) containing the linker represented by thegeneral formula (2) is deprotected (-Tr) to obtain the solid-phasecarrier (Am-2). Then, the amidite monomer (Am-1) and the solid-phasecarrier (Am-2) are subjected to a condensation reaction to obtain areaction product (Am-3). Then, the reaction product (Am-3) is oxidizedto obtain the product (Am-4). Then, the product (Am-4) is deprotected(-Tr) to obtain the product (Am-5). Then, the amidite monomer (Am-1) andthe product (Am-5) are further subjected to a condensation reaction toelongate the phosphodiester bond.

As described above, the hydroxyl group of the 5′position at the end ofthe elongated oligonucleotide strand is repeatedly subjected to a seriesof cycle including deprotection, condensation reaction and oxidation asmany times as necessary so as to provide a desired sequence, and thenthe resulting product can be cleaved from the solid-phase carrier toproduce a nucleic acid molecule having a desired sequence.

More specifically, a nucleic acid is prepared according to a preparationmethod comprising the following steps:

step (A): a step of deprotecting the protecting group of the hydroxylgroup at the 5′position of the nucleoside using the inorganic porouscarrier wherein R_(b) in the general formula (2) represents a nucleosideor nucleotide in which a hydroxyl group as a reactive group isprotected;

step (B): a condensation step of subjecting the hydroxyl group at the5′position of the nucleoside produced in the step (A) to a condensationreaction with an amidite compound having a second nucleoside base toproduce a phosphite;

step (C): an oxidation step of oxidizing the phosphite produced in thestep (B) to produce a nucleotide; and

step (D): a step of deprotecting the protecting group of the hydroxylgroup at the 5′position of the nucleotide produced in the step (C).

The preparation method comprising the above-mentioned steps (A) to (D)may optionally comprise the following steps:

step (B′): a step of further subjecting the product produced in the step(D) to a condensation reaction with an amidite compound having anucleoside base to be introduced in next time to produce a phosphite;

step (C′): a step of oxidizing the phosphite produced in the step (B′)to produce an oligonucleotide;

step (D′): a step of deprotecting the protecting group of the hydroxylgroup at the 5′position in the end of the oligonucleotide strandproduced in the step (C′); and step (E): a step of carrying out a seriesof steps consisting of the above step (B′), step (C′) and step (D′)repeatedly m times (wherein m is an integer of 1 or more) to react thenumber of m of amidite compounds (nucleic acid elongation reaction), andthen cleaving an elongated nucleic acid.

The nucleic acid elongation reaction of the present embodiment can becarried out according to the procedure of a general phosphoramiditemethod.

The “nucleic acid elongation reaction” herein refers to a reaction inwhich a nucleic acid strand, particularly RNA strand, is elongated bysequentially binding nucleotides through a phosphodiester bond. Thenucleic acid elongation reaction may be carried out by means of anautomatic nucleic acid synthesizer or the like that employs thephosphoramidite method.

In the deprotection step, the protecting group of the hydroxyl group atthe 5′position in the end of the RNA strand supported on the solid-phasecarrier is deprotected. As a general protecting group, a trityl-basedprotecting group (typically, a DMTr group) is used. The deprotection canbe carried out with an acid. Examples of the acid for deprotectioninclude trifluoroacetic acid, trichloroacetic acid, dichloroacetic acid,trifluoromethanesulfonic acid, methanesulfonic acid, hydrochloric acid,acetic acid, p-toluenesulfonic acid.

In the condensation step, the nucleoside phosphoramidite is bound to thehydroxyl group at the 5′position in the end of the RNA strand which isdeprotected by the above-mentioned deprotection step so as to producethe phosphite. As the nucleoside phosphoramidite, a nucleosidephosphoramidite in which the hydroxyl group at the 5′position isprotected with a protecting group (for example, DMTr group) is used.

Further, the condensation step can be carried out with an activatorwhich activates the nucleoside phosphoramidite. Examples of theactivator include 5-benzylthio-1H-tetrazole (BTT), 1H-tetrazole,4,5-dicyanoimidazole (DCI), 5-ethylthio-1H-tetrazole (ETT),N-methylbenzimidazolium triflate (N-MeBIT), benzimidazolium triflate(BIT), N-phenylimidazolium triflate (N-PhIMT), imidazolium triflate(IMT), 5-nitrobenzimidazolium triflate (NBT), 1-hydroxybenzotriazole(HOBT), 5-(bis-3,5-trifluoromethylphenyl)-1H-tetrazole (Activator-42),and the like, or a mixture of two or more thereof.

After the condensation step, an unreacted hydroxyl group at the5′position may be capped as needed. The capping can be carried out witha publicly known capping solution such as aceticanhydride-tetrahydrofuran solution, phenoxyacetic acid/N-methylimidazolesolution, and the like, or a mixture of two or more thereof.

The oxidation step refers to a step of oxidizing the phosphite formed bythe condensation step. The oxidation step can be carried out with anoxidizing agent. Examples of the oxidizing agent include iodine,m-chloroperbenzoic acid, tert-butylhydroperoxide, 2-butanoneperoxide,bis(trimethylsilyl)peroxide, 1,1-dihydroperoxycyclododecane, hydrogenperoxide, and the like, or a mixture of two or more thereof.

The oxidation step may be carried out after the capping operation asdescribed above, or conversely, the capping operation may be carried outafter the oxidation step, and accordingly an order of them is notlimited thereto.

After the oxidation step, the method returns to the deprotection step,and the above-mentioned steps including condensation reaction, oxidationand deprotection can be repeated depending on a nucleotide sequence ofRNA to be synthesized so as to synthesize RNA having a desired sequence.

After the synthesis of the RNA strand having the desired sequence iscompleted, the RNA strand is cleaved from the solid-phase carrier byammonia, amines, or the like, and collected.

Examples of the amines as describe above include methylamine,ethylamine, isopropylamine, ethylenediamine, diethylamine,triethylamine, and the like, or a mixture of two or more thereof.

When the universal linker is used, after the completion of the synthesisof RNA strand, the RNA strand is cleaved from the solid-phase carrier byammonia, amines, or the like, and the universal linker is eliminatedwith a nucleophile. Once the elimination is completed, the 3′position ofa terminal nucleotide is changed to a hydroxyl group, and the phosphateis bound to the universal linker to form a cyclic phosphodiester. Thecollected RNA may be purified by a publicly known method, as needed.

With respect to the inorganic porous carrier according this embodimentas described above, it is adopted a solid-phase carrier wherein in aparticular pore distribution, that is, a most frequent value (modediameter) of a pore is included in the range of 0.04 μm to 1 μm, andalso a cumulative pore volume ratio of cumulative pore volume (VB) whosepore size being within a range of 0.004 μm to 0.04 μm relative tocumulative pore volume (VA) whose pore size being within a range of 0.04μm to 1 μm is 30% or less. The solid-phase carrier exists with a highhomogeneity of pore having appropriate diameter with respect to theelongation of the target strand length, and contains very small amountof a pore having inappropriate (small with respect to a target strandlength) diameter. In the pore having inappropriate pore diameter (smalldiameter), an elongation reaction is likely to stop on the way to thetarget. Accordingly, the solid-phase carrier according to thisembodiment can easily elongate to a target strand length, and as aresult, a purity is further improved in a preparation of RNA.Particularly, a reduction of impurities at the beginning of oligonucleicacid synthesis can be drastically achieved. Also the method forpreparing RNA according to this embodiment can improve a purity in apreparation of RNA, and particularly, a long-stranded RNA can beobtained stably in high purity.

In addition, when the inorganic porous carrier of the present embodimentis applied to the nucleic acid synthesis, highly pure RNA can beobtained, even if long-stranded RNA of 40-mer or more is synthesized.The upper limit of the strand length of the RNA strand is notparticularly limited, and may be, for example, 200 mer or less or 150mer or less.

The “purity of RNA” herein refers to a percentage (%) at which thenucleic acid having the target strand length is obtained. It isdetermined based on an area percentage (that is, a percentage ofmeasured area) or a 10% width of a main peak in a chromatogram obtainedby liquid chromatography.

EXAMPLES

Hereinafter, the present invention is described in more detail withreference to Examples, however, the present invention should not belimited to these examples.

<Preparation of Inorganic Porous Substance>

Each of SP (1) to SP (10) as described below was used as the inorganicporous substance. In each of the inorganic porous substances SP (1) toSP (10), the most frequent value of the pore size (mode diameter; μm),the particle size (median diameter; μm), the cumulative pore volumeratio (%), the pore volume per volume (mL/mL), the specific surface areaper volume (m²/mL), and the porosity (%) were determined. The resultsare shown in Table 1.

The pore size (mode diameter; μm), the pore volume per volume (mL/mL),and the porosity (%) were determined respectively by a mercury intrusionmethod. The particle size (μm) was determined based on the mediandiameter measured by laser diffraction (scattering type). The specificsurface area per volume (m²/mL) was determined by multiplying the bulkdensity (g/mL), which was measured by the mercury intrusion method, bythe specific surface area per mass the inorganic porous substance(m²/g), which was measured by N₂ adsorption/desorption isothermmeasurement.

Inorganic Porous Substance SP (1):

A molded zeolite substance was obtained in the same manner as in Example1 described in JP 5875843 B2. The resulting molded zeolite substance wassuspended in a solvent of acetonitrile to prepare a suspension. Then,the suspension was sieved with a JIS sieve having an opening size of 125μm and successively with a JIS sieve having an opening size of 38 μm.Then, the powdery solid remaining on the sieve having an opening size of38 μm was dried by air at room temperature to prepare the inorganicporous substance SP (1) as a white powdery solid.

Inorganic Porous Substance SP (2):

In a stainless steel autoclave with a capacity of 1.5 L, tetraethylorthosilicate [Si(OC₂H₅)₄] 115 g, 40% by mass tetra-n-propyl ammoniumhydroxide aqueous solution 67 g, potassium hydroxide (purity 85%) 0.7 gand water 317 g were placed, and the mixture was vigorously stirred atroom temperature for 120 minutes. The molar ratios of water,tetra-n-propyl ammonium ion, hydroxide ion and potassium ion to siliconin the obtained mixed solution were 36, 0.24, 0.27 and 0.048,respectively. The mixed solution was stirred at 105° C. for 48 hours ata rotation speed of 300 rpm, and subjected to a hydrothermal reaction.The resulting reaction mixture was filtered, and washed repeatedly withpure water until the pH of the filtrate was made 9.0 or less. Theobtained wet cake was dried at 110° C., and then pulverized in a mortar.The obtained pulverized substance was sieved with a sieve having anopening size of 2.36 mm and successively a sieve having an opening sizeof 1.00 mm. The obtained substance was calcined in a tubular furnace at530° C. for 1 hour under nitrogen flow, and then further calcined at530° C. for 1 hour under flow of a mixed gas of nitrogen and air[nitrogen: air (volume ratio)=9:1] to obtain a white calcined substance.

Next, 10 g of the calcined substance as obtained above was put in apetri dish, and stood in a two-liter separable flask containing 100 mLof water, and the separable flask was closed with a lid. Then, theseparable flask was placed in a constant temperature water bath at 80°C. for 5 hours. The separable flask was taken out, and allowed to coolto 20° C. The resulting solid 8 g was placed in an autoclave, and amixed solution 222 g of 7.5% by mass ammonium nitrate aqueous solution88 g and 25% by mass ammonia aqueous solution 134 g was added thereto,and the mixture was stirred at 90° C. for 1 hour, and then the solid wasseparated by filtration. The solid was further treated with the mixedsolution of the ammonium nitrate aqueous solution and the ammoniaaqueous solution prepared in the same manner as described aboverepeatedly twice, and then washed with water, and dried. Finally, theobtained white solid was pulverized in a mortar, and sieved with sieveshaving an opening size of 106 μm and successively an opening size of 38μm to obtain the inorganic porous substance SP (2).

Inorganic Porous Substance SP (3):

In a stainless steel autoclave with a capacity of 1.5 L, tetraethylorthosilicate [Si(OC₂H₅)₄] 155 g, 40% by mass tetra-n-propyl ammoniumhydroxide aqueous solution 136 g, potassium hydroxide (purity 85%) 0.3 gand water 162 g were placed, and the mixture was vigorously stirred atroom temperature for 120 minutes. The molar ratios of water,tetra-n-propyl ammonium ion, hydroxide ion and potassium ion to siliconin the obtained mixed solution were 18, 0.36, 0.38 and 0.048,respectively. The mixed solution was stirred at 105° C. for 48 hours ata rotation speed of 300 rpm, and subjected to a hydrothermal synthesisreaction. The resulting reaction mixture was filtered, and washedrepeatedly with pure water until the pH of the filtrate was made 9.0 orless. The obtained wet cake was dried at 110° C., and then pulverized ina mortar. The obtained pulverized substance was sieved with a sievehaving an opening size of 2.36 mm and successively a sieve having anopening size of 1.00 mm. The obtained substance was calcined in atubular furnace at 530° C. for 1 hour under nitrogen flow, and thenfurther calcined at 530° C. for 1 hour under flow of a mixed gas ofnitrogen and air [nitrogen: air (volume ratio)=9:1] to obtain a whitecalcined substance.

Next, 10 g of the calcined substance as obtained above was put in apetri dish, and stood in a two-liter separable flask containing 100 mLof water, and the separable flask was closed with a lid. Then, theseparable flask was placed in a constant temperature water bath at 80°C. for 5 hours. The separable flask was taken out, and allowed to coolto 20° C. The resulting solid 8 g was placed in an autoclave, and amixed solution 222 g of 7.5% by mass ammonium nitrate aqueous solution88 g and 25% by mass ammonia aqueous solution 134 g was added thereto,and the mixture was stirred at 90° C. for 1 hour, and then the solid wasseparated by filtration. The solid was further treated with the mixedsolution of the ammonium nitrate aqueous solution and the ammoniaaqueous solution prepared in the same manner as described aboverepeatedly twice, and then washed with water, and dried. Finally, theobtained white solid was pulverized in a mortar, and sieved with sieveshaving an opening size of 106 μm and successively an opening size of 38μm to obtain the inorganic porous substance SP (3).

Inorganic Porous Substance SP (4):

In a stainless steel autoclave with a capacity of 1.5 L, tetraethylorthosilicate [Si(OC₂H₅)₄] 115 g, 40% by mass tetra-n-propyl ammoniumhydroxide aqueous solution 57 g, potassium hydroxide (purity 85%) 0.9 gand water 325 g were placed, and the mixture was vigorously stirred atroom temperature for 120 minutes. The molar ratios of water,tetra-n-propyl ammonium ion, hydroxide ion and potassium ion to siliconin the obtained mixed solution were 36, 0.20, 0.24 and 0.048,respectively. The mixed solution was stirred at 105° C. for 48 hours ata rotation speed of 300 rpm, and subjected to a hydrothermal synthesisreaction. The resulting reaction mixture was filtered, and washedrepeatedly with pure water until the pH of the filtrate was made 9.0 orless. The obtained wet cake was dried at 110° C., and then pulverized ina mortar. The obtained pulverized substance was sieved with a sievehaving an opening size of 2.36 mm and successively a sieve having anopening size of 1.00 mm. The obtained substance was calcined in atubular furnace at 530° C. for 1 hour under nitrogen flow, and thenfurther calcined at 530° C. for 1 hour under flow of a mixed gas ofnitrogen and air [nitrogen: air (volume ratio)=9:1] to obtain a whitecalcined substance.

Next, 10 g of the calcined substance as obtained above was put in apetri dish, and stood in a two-liter separable flask containing 100 mLof water, and the separable flask was closed with a lid. Then, theseparable flask was placed in a constant temperature water bath at 80°C. for 5 hours. The separable flask was taken out, and allowed to coolto 20° C. The resulting solid 8 g was placed in an autoclave, and amixed solution 222 g of 7.5% by mass ammonium nitrate aqueous solution88 g and 25% by mass ammonia aqueous solution 134 g was added thereto,and the mixture was stirred at 90° C. for 1 hour, and then the solid wasseparated by filtration. The solid was further treated with the mixedsolution of the ammonium nitrate aqueous solution and the ammoniaaqueous solution prepared in the same manner as described aboverepeatedly twice, and then washed with water, and dried. Finally, theobtained white solid was pulverized in a mortar, and sieved with sieveshaving an opening size of 106 μm and successively an opening size of 38μm to obtain the inorganic porous substance SP (4).

Inorganic Porous Substance SP (5):

A commercial spherical silica dispersion solution (Product name:Seehoster KE-W30, manufactured by Nippon Shokubai Co. Ltd.) 30 mL wasdried at 80° C. to obtain a solid in a massive form. The obtained solidswere calcined at 800° C. for 3 hours, and pulverized in a mortar, toobtain a powdered solid. The obtained powdered solids were suspended inacetonitrile solvent, and after that, the resulting suspension solutionswere sieved with sieves having an opening size of 38 μm. The powderedsolids remained on the sieve were air dried at room temperature toobtain the inorganic porous substance SP (5) 4 g as a white powderedsolid.

Inorganic Porous Substance SP (6):

A calcined zeolite substance was obtained in the same manner as inExample 1 described in JP 5875843B2. Then, 10 g of the resultingcalcined substance was put in a petri dish, and stood in a two-literseparable flask containing 100 mL of water, and the separable flask wasclosed with a lid. Then, the separable flask was placed in a constanttemperature water bath at 80° C., and left to stand for 24 hours. Theseparable flask was taken out, and allowed to cool to 20° C. Theresulting solid 8 g was placed in an autoclave, and a mixed solution 222g of 7.5% by mass ammonium nitrate aqueous solution 88 g and 25% by massammonia aqueous solution 134 g was added thereto, and the mixture wasstirred at 90° C. for 1 hour, and then the solid was separated byfiltration. The solid was further treated with the mixed solution of theammonium nitrate aqueous solution and the ammonia aqueous solutionprepared in the same manner as described above repeatedly nine times,and then washed with water, and dried to obtain the inorganic poroussubstance SP (6).

Inorganic Porous Substance SP (7):

In a stainless steel autoclave with a capacity of 1.5 L, tetraethylorthosilicate [Si(OC₂H₅)₄] 115 g, 40% by mass tetra-n-propylammoniumhydroxide aqueous solution 57 g, potassium hydroxide (purity 85%) 0.9 gand water 325 g were placed, and the mixture was vigorously stirred atroom temperature for 120 minutes. The molar ratios of water,tetra-n-propylammonium ion, hydroxide ion and potassium ion to siliconin the obtained mixed solution were 36, 0.20, 0.24 and 0.048,respectively. The mixed solution was stirred at 105° C. for 48 hours ata rotation speed of 300 rpm, and subjected to a hydrothermal synthesisreaction. The resulting reaction mixture was filtered, and washedrepeatedly with pure water until the pH of the filtrate was made 9.0 orless. The obtained wet cake was dried at 110° C., and then pulverized ina mortar. The obtained pulverized substance was sieved with a sievehaving an opening size of 2.36 mm and successively a sieve having anopening size of 1.00 mm. The obtained substance was calcined in atubular furnace at 530° C. for 1 hour under nitrogen flow, and thenfurther calcined at 530° C. for 1 hour under flow of a mixed gas ofnitrogen and air [nitrogen: air (volume ratio)=9:1] to obtain a whitecalcined substance.

Next, 10 g of the calcined substance as obtained above was put in apetri dish, and stood in a two-liter separable flask containing 100 mLof water, and the separable flask was closed with a lid. Then, theseparable flask was placed in a constant temperature water bath at 80°C. for 5 hours. The separable flask was taken out, and allowed to coolto 20° C. The resulting solid 8 g was placed in an autoclave, and amixed solution 222 g of 7.5% by mass ammonium nitrate aqueous solution88 g and 25% by mass ammonia aqueous solution 134 g was added thereto,and the mixture was stirred at 90° C. for 1 hour, and then the solid wasseparated by filtration. The solid was further treated with the mixedsolution of the ammonium nitrate aqueous solution and the ammoniaaqueous solution prepared in the same manner as described aboverepeatedly twice, and then washed with water, and dried. Finally, theobtained white solid was pulverized in a mortar, and sieved with sieveshaving an opening size of 106 μm and successively an opening size of 38μm to obtain the inorganic porous substance SP (7).

Inorganic Porous Substance SP (8):

A porous silica was prepared by referring to a preparation method of adouble pore porous substance in Example 1 described in JP 2010-120780A1.

Ethylene-propylene-glycol brock co-polymer (Product name: Pluronic P123,manufactured by BASF Co. Ltd.) 5.5 g was dissolved in 0.01 M aqueousacetic acid solution 40 mL, and then urea 2.5 g was dissolved thereto.To the aqueous solution was added tetraethoxysilane 25 mL, and themixture was stirred for 1 hour to obtain a solution. The resultingsolution was left to stand at 60° C. for 24 hours to obtain a gel, andthe gel was washed with methanol-water. The obtained gel was dried at60° C., and calcined at 250° C. for 10 hours to an inorganic poroussubstance (8) as a porous silica powder.

Inorganic Porous Substance SP (9):

In a stainless steel autoclave with a capacity of 1600 L, tetraethylorthosilicate [Si(OC₂H₅)₄] 186 kg, 40% by mass tetra-n-propylammoniumhydroxide aqueous solution 166 kg, potassium hydroxide (purity 85%) 0.3kg and water 490 kg were placed, and the mixture was vigorously stirredat room temperature for 120 minutes. The molar ratios of water,tetra-n-propylammonium ion, hydroxide ion and potassium ion to siliconin the obtained mixed solution were 37, 0.36, 0.39 and 0.049,respectively. The mixed solution was stirred at 105° C. for 12 hours ata rotation speed of 60 rpm, and subjected to a hydrothermal synthesisreaction. The resulting reaction mixture was washed with pure watersimilarly to the above-mentioned method for preparing Inorganic poroussubstance SP (2). After washing, a slurry containing crystals wasrecovered. The slurry was spray-dried with an Atomizer-type spray dryerto mold it to a particle form. The resulting products were calcined at550° C. for 2.5 hours under nitrogen flow, and next, were calcined at550° C. for 2.5 hours under a mixed gas flow [nitrogen: air (byvolume)=3:1] to obtain a calcined product as white substance.

Inorganic Porous Substance SP (10):

As the inorganic porous substance SP (10), a commercially availablespherical silica gel powder (trade name: M.S.GEL, produced by AGCSi-Tech Co., Ltd.) was used.

[Measurement of Pore Distribution by Mercury in Method]

With respect to the inorganic porous substance SP (10) to the inorganicporous substance SP (4), a pore distribution of about 0.004 to 200 μm ofpore size (value obtained by calculating differentially a pore volume bya pore size) was determined by mercury intrusion method.

The above-mentioned measurement was used with AutoPoreIV9520(manufactured by Micromaritics). As a pretreatment, aconstant-temperature drying was carried out on the inorganic poroussubstance at 150° C. for 4 hours.

The pore size was calculated by the following equation (A).

$\begin{matrix}{{D = \text{?}}{\text{?}\text{indicates text missing or illegible when filed}}} & (A)\end{matrix}$

P: Pressure, D: Pore Diameter, σ: Surface tension of mercury, θ: Contactangle between mercury and sample.

In this measurement, the surface tension of mercury: a was 0.48 N/m, andthe contact angle between mercury and sample was 140°.

By measuring a pore distribution by the above-mentioned mercuryintrusion method, the most frequent value of pore size (mode diameter,μm), a porosity (%), and a cumulative pore volume ratio of cumulativepore volume (VB) whose pore size being within a range of 0.004 μm to0.04 μm relative to cumulative pore volume (VA) whose pore size beingwithin a range of 0.04 μm to 1 μm, respectively were determined. Theresults are shown in Table 1.

Most Frequent Value (Mode Diameter):

The most frequent value of pore size was determined from a value ofX-axis at a peak top in the pore size distribution obtained by themercury intrusion method (a graph in which the X-axis is a value of thepore size and the Y-axis is a value obtained by differentiating the porevolume by the pore size).

The porosity ratio (%) was calculated by multiplying the bulk density(g/mL) with the cumulative pore volume (mL/g) which is included within arange of 0.004 μm to 200 μm.

Cumulative Pore Volume Ratio:

The cumulative pore volume ratio (%) was calculated by the followingequation: VB/VA×100.

<Silane Coupling Agent>

As the silane coupling agent, the ingredient (C1) and ingredient (C2) asdescribed below were used.

Ingredient (C1):

3-Aminopropyldiisopropylethoxysilane which was commercially availablewas purchased and used.

Ingredient (C2):

3-Aminopropyltriethoxysilane (TCI, CAS RN: 919-30-2, product code:A0439) was used.

<Method for Preparing Inorganic Porous Substance (Inorganic PorousCarrier) which Supports a Linker>

The inorganic porous carrier of each of examples was obtained bytreating the surface of any one of the inorganic porous carriers SP (1)to SP (10) as produced above with any one of the ingredients (C1) to(C2) as the silane coupling agents.

Example 1

The inorganic porous substance SP (1) 2.00 g was placed in a four-neckedflask, and toluene 100 mL was added thereto. The ingredient (C1) 4.8 mgwas further added thereto under stirring, and the mixture was stirred atroom temperature for 3 hours. Then, the reaction solution was filtered,and washed with toluene, and then the residue was dried under reducedpressure to obtain the inorganic porous carrier of Example 1.

Example 2

The inorganic porous carrier of Example 2 was obtained in the samemanner as the preparation method of Example 1 except for that theinorganic porous substance SP (1) was replaced with the inorganic poroussubstance SP (2) (2.00 g).

Example 3

The inorganic porous carrier of Example 3 was obtained in the samemanner as the preparation method of Example 1 except for that theinorganic porous substance SP (1) was replaced with the inorganic poroussubstance SP (3) (2.00 g) and the addition amount of the ingredient (C1)was changed to 6.8 mg.

Example 4

The inorganic porous carrier of Example 4 was obtained in the samemanner as the preparation method of Example 1 except for that theinorganic porous substance SP (1) was replaced with the inorganic poroussubstance SP (4) (2.00 g) and the addition amount of the ingredient (C1)was changed to 4.5 mg.

Example 5

The inorganic porous carrier of Example 5 was obtained in the samemanner as the preparation method of Example 1 except for that theinorganic porous substance SP (1) was replaced with the inorganic poroussubstance SP (5) (1.00 g) and the addition amount of the ingredient (C1)was changed to 2.4 mg.

Example 6

The inorganic porous carrier of Example 6 was obtained in the samemanner as the preparation method of Example 1 except for that theinorganic porous substance SP (1) was replaced with the inorganic poroussubstance SP (6) (2.00 g) and the addition amount of the ingredient (C1)was changed to 6.8 mg.

Example 7

The inorganic porous carrier of Example 7 was obtained in the samemanner as the preparation method of Example 1 except for that theinorganic porous substance SP (1) was replaced with the inorganic poroussubstance SP (7) (0.40 g) and the addition amount of the ingredient (C1)was changed to 1.2 mg.

Example 8

The inorganic porous carrier of Example 8 was obtained in the samemanner as the preparation method of Example 1 except for that theinorganic porous substance SP (1) was replaced with the inorganic poroussubstance SP (9) (1.00 g) and the addition amount of the ingredient (C1)was changed to 7.0 mg.

Example 9

The inorganic porous carrier of Example 9 was obtained in the samemanner as the preparation method of Example 1 except for that theinorganic porous substance SP (1) was replaced with the inorganic poroussubstance SP (10) (1.00 g) and the addition amount of the ingredient(C1) was changed to 2.4 mg.

Comparative Example 1

The inorganic porous carrier of Comparative Example 1 was obtained inthe same manner as the preparation method of Example 1 except for thatthe inorganic porous substance SP (1) was replaced with the inorganicporous substance SP (8) (2.42 g) and the ingredient (C1) was replacedwith the ingredient (C2) (44.7 mg).

Comparative Example 2

The inorganic porous carrier of Comparative Example 2 was obtained inthe same manner as the preparation method of Example 1 except for thatthe inorganic porous substance SP (1) was replaced with the inorganicporous substance SP (8) (2.00 g) and the addition amount of theingredient (C1) was changed to 1.2 mg.

Comparative Example 3

The inorganic porous carrier of Comparative Example 3 was obtained inthe same manner as the preparation method of Example 1 except for thatthe inorganic porous substance SP (1) was replaced with the inorganicporous substance SP (8) (2.00 g) and the addition amount of theingredient (C1) was changed to 1.2 mg (which was the same as theinorganic porous carrier of comparative example 2).

<Preparation of Solid-Phase Carrier>

U-succinate(5′-O-dimethoxytrityl-2′-O-tert-butyldimethylsilyl-3′-O-succinyluridine)25.1 mg, 1-[bis(dimethylamino)methylene]-1H-1,2,3-benzotriazolium3-oxide hexafluorophosphate (HBTU) 12.5 mg, N,N-diisopropylethylamine5.9 μL and acetonitrile 2.7 mL were mixed, and the inorganic porouscarrier 300.0 mg of each of Examples 1 to 10 and Comparative Examples 1to 4 was added to the mixture.

The mixture was left to stand at 25° C. for 18 hours, and then filtered,and the solid (residue) was washed with acetonitrile 10 mL. A solution 1mL of acetic anhydride and 2,6-lutidine in THF (volume ratio of aceticanhydride/2,6-lutidine/THF: 1/1/8) and a solution 1 mL of N-methylimidazole in THF (volume ratio of N-methyl imidazole/THF: 16/84) wereadded to the washed solid. The mixture was left to stand for 1 minute,and then filtered, and the solid was washed with acetonitrile 10 mL. Thewashed solid was dried under vacuum to obtain the solid-phase carrier inwhich the nucleoside was supported on the inorganic porous carrier.

An aqueous 70% perchloric acid solution was diluted with methanol toprepare a solution of 30% perchloric acid/methanol. The solid-phasecarrier 10 mg which supported the nucleoside, as prepared above, wasplaced in a measuring flask, and was diluted to 10 mL with the solutionof 30% perchloric acid/methanol. The resulting solution was furtherdiluted 10-fold with the solution of 30% perchloric acid/methanol, andthen an absorbance thereof at 498 nm was measured, and the supportdensity of nucleoside was calculated based on the following formula. Theresults are shown in Table 1.

${{Support}\mspace{14mu}{Density}\mspace{14mu}{of}\mspace{14mu}{{Nucleoside}\left\lbrack {{µmol}/m^{2}} \right\rbrack}} = \frac{\left( {14.3 \times \left( {{Absorbance}\mspace{14mu}{at}{\mspace{11mu}\;}498\mspace{14mu}{nm}} \right) \times 10 \times 10} \right)}{\begin{matrix}{\left( {{Mass}\mspace{14mu}{of}\mspace{14mu}{Soli}\text{d-p}{hase}\mspace{14mu}{{Carrier}({mg})}} \right) \times} \\\left( {{Specific}\mspace{14mu}{Surface}\mspace{14mu}{Area}\mspace{14mu}{of}\mspace{14mu}{Inorganic}\mspace{14mu}{Porous}\mspace{14mu}{{{Carrier}\left( {m^{2}/g} \right)} \div 1000}} \right)\end{matrix}}$

<Solid-Phase Synthesis of Oligonucleic Acid>

Sequence (A): (SEQ ID NO: 1, 2) 5′-GCAGAGUACACACAGCAUAUACC-P-GGUAUAUGCUGUGUGUACUCUGCUU-3′ (49-mer). (SEQ ID NO: 1)GCAGAGUACACACAGCAUAUACC and (SEQ ID NO: 2) GGUAUAUGCUGUGUGUACUCUGCUU.Sequence (B): (SEQ ID NO: 3)5′-AUAACUCAAUUUGUAAAAAAGUUUUAGAGCUAGAAAUAGCAAGUUAAAAUAAGGCUAGUCCGUUAUCAACUUGAAAAAGUGGCACCGAGUCGGUG CUUUUUUU-3′ (103-mer).

In the above sequence (A), P represents a binding moiety separated withwavy lines in the following structure.

The oligonucleotide consisting of the sequence (A) or the sequence (B)was synthesized from the 3′side to the 5′side according to thephosphoramidite method by means of a nucleic acid synthesizer (tradename: NTS M-4-MX-E, produced by Nihon Techno Service Co., Ltd.) (See thereaction route (condensation reaction, oxidation, and deprotection asdescribed above)).

Each of solid-phase carriers as prepared above was used for the abovesolid-phase synthesis.

As the amidite monomer, the adenosine EMM amidite (described in Example4 of US2012/035246 A1), the cytidine EMM amidite (described in Example 3of the same US patent literature), the guanosine EMM amidite (describedin Example 5 of the same US patent literature), the uridine EMM amidite(described in Example 2 of the same US patent literature) and amidite P(described in WO2017/188042 A1) as shown below were used.

Further, in the solid-phase synthesis, a solution of high puritytrichloroacetic acid in toluene was used as a deblocking solution,5-benzylmercapto-1H-tetrazole was used as a condensing agent, an iodinesolution was used as an oxidizing agent, and a phenoxyacetic acidsolution and an N-methyl imidazole solution were used as a cappingsolution.

The solid-phase carrier after the completion of synthesis was placed ina glass vial with a lid, and a solution of 28% NH₄OH and EtOH at a ratioof 1:1 to 2:1 was added thereto. Then, the mixture was left to stand at40° C. for 4 hours. The solution after the completion of reaction wasfiltered, and washed with water and EtOH successively. The resultingsolution was dried to obtain a crude oligonucleotide having a protectedgroup. Then, the crude oligonucleotide was deprotected by the treatmentwith tetra-n-butyl ammonium fluoride (TBAF) in the presence ofnitromethane to obtain the crude product.

[Measurement of Oligonucleic Acid Purity]

The determination of the purity of oligonucleic acid was carried out byhigh performance liquid chromatography HPLC (wavelength 260 nm, columnDNAPac™ PA100 4×250 mm).

The above-mentioned crude products were separated into each ofingredients by the above HPLC, and then the purity of oligonucleic acidwas calculated from a percentage of area value of main product having atarget strand length relative to the total area value of the obtainedchromatogram. The results are shown in Table 1.

TABLE 1 Inorganic Porous Carrier Carrier represented by General Formula(l) Pore Particle Cumu- Density Purity of Inor- Size Size lative PoreSurface of Oligonucleic ganic mode median Pore Volume Area Nucle- ChainAcid (%) Porous diam- diam- Volume per per oside Length of Half ValueSub- Sub- n = 1 eter eter Ratio Volume Volume Porosity (μmol/Oligonucleic Width of stance stance R, R L (μm) (μm) (%) (mL/mL) (m²/mL)(%) m²) Acid Main Peak Example SP(1) Zeo- Isopro- CH₂ 0.081 48 7.9 0.298.4 69 0.65 49mer 57.8 1 lite pyl (RNA) Group Example SP(2) Zeo- Isopro-CH₂ 0.078 72 15.3 0.32 11.3 76 0.36 49mer 46.2 2 lite pyl (RNA) GroupExample SP(3) Zeo- Isopro- CH₂ 0.052 85 20.2 0.24 13.8 81 0.48 49mer54.9 3 lite pyl (RNA) Group Example SP(4) Zeo- Isopro- CH₂ 0.1 68 15.70.23 6.1 79 0.4 49mer 46.2 4 lite pyl (RNA) Group Example SP(5) SilicaIsopro- CH₂ 0.06 82 16.4 0.18 8.9 65 0.49 49mer 54.5 5 Gel pyl (RNA)Group Example SP(6) Zeo- Isopro- CH₂ 0.11 48 9.6 0.34 7.7 78 1.03 103mer38.1 6 lite pyl (RNA) Group Example SP(7) Zeo- Isopro- CH₂ 0.16 48 11.10.27 9.9 80 0.49 103mer 31.6 7 lite pyl (RNA) Group Example SP(9) Zeo-Isopro- CH₂ 0.071 62 16.0 0.38 13.8 85 0.68 49mer 42.8 8 lite pyl (RNA)Group Example SP(10) Silica Isopro- CH₂ 0.11 40 5.9 0.38 5.8 81 0.7149mer 50.5 9 Gel pyl (RNA) Group Compara- SP(8) Silica Ethoxy CH₂ 0.1349 31.9 0.29 57 77 0.33 49mer 39.2 tive Gel Group (RNA) Example 1Compara- SP(8) Silica Isopro- CH₂ 0.13 49 31.9 0.26 57 77 0.17 49mer39.2 tive Gel pyl (RNA) Example Group 2 Compara- SP(8) Silica Isopro-CH₂ 0.13 49 31.9 0.26 57 77 0.17 103mer 48.2 tive Gel pyl (RNA) ExampleGroup 3

According to the results shown in Table 1, it is possible to confirmthat the purity of the oligonucleic acid is higher in the case of use ofthe solid-phase carriers of Examples 1 to 9 than in the case of use ofthe solid-phase carriers of Comparative Examples 1 to 3.

Accordingly, it is possible to conclude that the solid-phase carrierused in the present invention can further improve the purity in thepreparation of nucleic acid.

INDUSTRIAL APPLICABILITY

The present invention provides a method for preparing nucleic acid,which can improve the purity even in the synthesis of long-strandednucleic acid. The nucleic acid obtained by the inorganic porous carrierand the preparation method using the same is useful as a raw materialfor pharmaceutical products.

Sequence Listing Free Text

SEQ ID NOs: 1 to 3 in the sequence listing represent the base sequencesof oligonucleotides prepared according to the preparation method of thepresent invention.

Sequence Listing

1. An inorganic porous carrier that comprises a linker represented bygeneral formula (1), wherein a most frequent value (mode diameter) in apore distribution as measured by mercury intrusion method is 0.04 μm to1 μm, and also a cumulative pore volume ratio of cumulative pore volume(VB) whose pore size being within a range of 0.004 μm to 0.04 μmrelative to cumulative pore volume (VA) whose pore size being within arange of 0.04 μm to 1 μm is 30% or less.

[wherein, a bond marked with * represents a linkage to the oxygen atomof a silanol group in an inorganic porous substance; n is an integer of1, 2 or 3; R represents independently of each other an alkyl groupcontaining 3 to 10 carbon atoms which may optionally have a substituentselected from an alkoxy group and a fluorine atom; a phenyl group whichmay optionally have a substituent selected from an alkyl group, analkoxy group, and a fluorine atom; a hydroxyl group; or an alkoxy groupcontaining 1 to 4 carbon atom; and L represents a single bond; analkylene group of 1 to 20 carbon atoms; or an alkylene group containing2 to 20 carbon atoms which contains —CH₂-Q-CH₂— group wherein any groupQ selected from a group consisting of —O—, —NH—, —NH—CO— and —NH—CO—NH—is inserted into at least one of —CH₂—CH₂— group constituting thealkylene group; providing that a carbon atom of the methylene groupbound to the group Q does not bind to another group Q at the same time].2. An inorganic porous carrier that comprises a linker represented bygeneral formula (2), wherein a mode diameter in a pore distribution asmeasured by mercury intrusion method is 0.04 μm to 1 μm, and also acumulative pore volume ratio of cumulative pore volume (VB) whose poresize being within a range of 0.004 μm to 0.04 μm relative to cumulativepore volume (VA) whose pore size being within a range of 0.04 μm to 1 μmis 30% or less.

[wherein a bond marked with * represents a linkage to the oxygen atom ofa silanol group in an inorganic porous substance; n is an integer of 1,2 or 3; R represents independently of each other an alkyl groupcontaining 3 to 10 carbon atoms which may optionally have a substituentselected from an alkoxy group and a fluorine atom; a phenyl group whichmay optionally have a substituent selected from an alkyl group, analkoxy group, and a fluorine atom; a hydroxyl group; or an alkoxy groupcontaining 1 to 4 carbon atom; L represents a single bond; an alkylenegroup containing 1 to 20 carbon atoms; or an alkylene group containing 2to 20 carbon atoms which contains —CH₂-Q-CH₂— group wherein any group Qselected from the group consisting of —O—, —NH—, —NH—CO—, and —NH—CO—NH—is inserted into at least one —CH₂—CH₂— group constituting the alkylenegroup; providing that a carbon atom of the methylene group bound to thegroup Q doses not bind to another group Q at the same time; R_(b)represents a nucleotide or a nucleotide in which a reactive group isprotected or deprotected; and L₁ represents a divalent group bound to anoxygen atom of a primary or a secondary hydroxy group as R_(b).].
 3. Theinorganic porous carrier according to claim 2 wherein L¹ in the generalformula (2) is a succinyl linker or a universal linker.
 4. The inorganicporous carrier according to claim 1 wherein the specific surface areaper volume of the inorganic porous substance is within a range of 0.1m²/mL or more to 100 m²/mL or less.
 5. The inorganic porous carrieraccording to claim 1 wherein the pore volume per volume of the inorganicporous substance is within a range of 0.05 mL/mL or more to 0.6 mL/mL orless.
 6. The inorganic porous carrier according to claim 1 wherein theporosity of the inorganic porous substance is 50% or more.
 7. Theinorganic porous carrier according to claim 2 wherein a density of thegrafted linker is within a range of 0.1 μmol/m² or more to 5.0 μmol/m²or less relative to a specific surface area per mass of the inorganicporous substance.
 8. The inorganic porous carrier according to claim 1wherein the particle diameter (a median diameter) of the inorganicporous substance is within a range of 1 μm or more to 1000 μm or less.9. The inorganic porous carrier according to claim 1 wherein theinorganic porous substance is silica, silica gel, zeolite, or glass. 10.A method for preparing a nucleic acid which is carried out by using theinorganic porous carrier wherein R_(b) in the general formula (2)described in claim 2 represents a nucleoside or nucleotide in which ahydroxyl group as a reactive group is protected, wherein the methodcomprises the following steps: a step (A) of deprotecting a protectinggroup of the hydroxyl group at a 5′position of the nucleoside; a step(B) of subjecting the hydroxyl group at the 5′position of the nucleosideproduced in the step (A) to a condensation reaction with an amiditecompound having a second nucleoside base to produce a phosphite; a step(C) of oxidizing the phosphite produced in the step (B) to produce anucleotide; and a step (D) of deprotecting a protecting group of ahydroxyl group at a 5′position of the nucleotide produced in the step(C).
 11. The method according to claim 10 which further comprise thefollowing steps: a step (B′) of subjecting the product produced in thestep (D) to a condensation reaction with an amidite compound having anucleoside base to be introduced in next time to produce a phosphite; astep (C′) of oxidizing the phosphite produced in the step (B′) toproduce an oligonucleotide; and a step (D′) of deprotecting a protectinggroup of a hydroxyl group at a 5′position in an end of anoligonucleotide strand produced in the step (C′).
 12. The methodaccording to claim 11 which further comprise a step (E) of carrying outa series of steps consisting of the above step (B′), step (C′) and step(D′) repeatedly m times (wherein m is an integer of 1 or more) to reactthe number of m of amidite compounds, and then cleaving an elongatednucleic acid.
 13. (canceled)
 14. The inorganic porous carrier accordingto claim 2 wherein the specific surface area per volume of the inorganicporous substance is within a range of 0.1 m²/mL or more to 100 m²/mL orless.
 15. The inorganic porous carrier according to claim 2 wherein thepore volume per volume of the inorganic porous substance is within arange of 0.05 mL/mL or more to 0.6 mL/mL or less.
 16. The inorganicporous carrier according to claim 2 wherein the porosity of theinorganic porous substance is 50% or more.
 17. The inorganic porouscarrier according to claim 2 wherein the particle diameter (a mediandiameter) of the inorganic porous substance is within a range of 1 μm ormore to 1000 μm or less.
 18. The inorganic porous carrier according toclaim 2 wherein the inorganic porous substance is silica, silica gel,zeolite, or glass.